I pressed mine and my wifes phone up to my ear in a very quiet room and ran a speed test and I could hear a ticking noise before the speed test and a hissing noise during the test on both phones. I couldn't hear it before due to the room not being quiet enough and not pressing my ear to the back. I suspect all 7s exhibit this to some extent. My iPod 6th gen does this as well. I never tried my 6s plus.